Abstract:

The increasingly prominent blockage problem caused by crystallization exists in tunnels′ drainage system in southwest China. In order to study the crystallization rule of drainpipe, based on the analysis results of groundwater and crystallization, PVC pipes are used to simulate the actual tunnel drainage pipes and four kinds of saturated solutions (with pH value 8,9,10,11, respectively) are prepared by pure CaCl2 and NaOH reagents. The 56-day growth crystallization tests with the four saturated solutions under two water-filling states (i. e. semi-filled and full-filled) are carried out respectively. Through analyzing of the crystalline, the XRD and SEM figures, the growth rule of crystallization in tunnel drainpipe is obtained. The results show that the amount of crystallization increases with pH value though it is coupling affected by pH value and water-filling condition. When the pH value is within 8~10, the amount of crystallization in semi-filled pipe is higher, and it is affected more greatly by the condition of water-filling. When the pH value is 11, after 23 days of test, the amount of crystallization in full-filled pipe gradually turns higher than that in the semi-filled pipe, and the amount of crystallization is primarily affected by the pH value. The crystallization samples used in the tests are all calcite, and the greater the pH value, the crystallization that appear mainly in spindle shape accumulate more compact and the size is smaller and more uniform.

Key words: alkaline environment, tunnel, pH values, water filled conditions, crystallization of drainpipes, XRD, SEM